Bladed rotors

ABSTRACT

A ROTOR COMPRISING TWO AXIALLY SPACED DISCS, A PLURALITY OF RADIALLY EXTENDING VANES BETWEEN THE DISCS WHICH JOIN THE DISCS TOGETHER, PREFERABLY THE VANES EXTEND BEYOND THE DISC AS LUGS WHICH DEFINE GUIDEWAYS FOR RECEIVING BLADES, WHEREBY THE RADIAL FORCE OF THE ROTATING BLADES IS TRANSMITTED IN TENSION TO THE VANES AND THEN AS A SHEAR LOADING INTO THE DISCS OVER A RELATIVELY LARGE AREA. IT IS ALSO PREFERABLE THAT ONE OF THE DISCS BE ANNULAR SO THAT COOLING AIR CAN ENTER AT THE INNER PERIPHERY AND BE IMPELLED THROUGH THE PASSAGEWAYS DEFINED BY THE VANES AND THEN ENTER THE BLADES THROUGH HOLES IN THE BASES OF THE TANGS.

United States Patent [72] Inventors Werner E. Howald 2,438,998 4/1948Halford 60/392 Cincinnati; 2,947,512 8/1960 Jones et a1. 415/114 1 N 'ggg' Mason 0M0 Primary Examiner-Samuel Feinberg [21] g M 16 I966Attorneys-Melvin M. Goldenberg,Frank L. Neuhauser, [22] e Oscar B.Waddell, E. S. Lee, 111, G. R. Powers and Derek P. [45] Patented June28, 1971 Lawrence [73] Assignee General Electric Comapny [54] BLADEDROTORS I 6 Claims, 5 Drawing Figs.

ABSTRACT: A rotor compnslng two axially spaced discs, a [52] U.S. Cl.416/96, m m f radially extending vanes between the discs which 416/97416/2M join the discs together; preferably the vanes extend beyond the[51] lnt.Cl. Fflld 5/08, disc as lugs which d fi guideways f receivingblades Fold 5/ whereby the radial force of the rotating blades istransmitted [50] Field ol Search 253/39.l5, in tension {0 the vanes andhen as a shear loading into the 39 (F-R); 416/961 97 discs over arelatively large area. It is also preferable that one of the discs beannular so that cooling air can enter at the [56] References CM innerperiphery and be impelled through the passageways UNITED STATES PATENTSdefined by the vanes and then enter the blades through holes 2,405,1908/1946 Darling 60/3917 in the bases of the tangs.

/l I' II KY\\\ \\\\m7 PATENTED JUH28 I97! SHEET 1 OF 2 INVENTORS WERNERE. HOWALD JACK D. WRIGHT PATENTEUJUH28IH7E 3588277 SHEET 2 OF 2INVENTORS WERNER E. HOWALD JACK o. WRIGHT BY "V k p 1 BLADED ROTORS Thepresent invention relates to improvements in bladed rotors employed inaxial flow turbines and compressors.

In gas turbine engines, particularly those employed for aircraftpropulsion, engine weight is of particular concern. One way in whichweight reduction can be obtained is to reduce the size and massofindividual components of the engine.

Toward this broad end of reducing gas turbine engine weight, one objectof the present invention is to substantially reduce the weight of theturbine rotor normally employed in such engines.

Another and broader-object of the invention is to provide an improvedturbine rotor which for a givensize and mass has greater strength,reliability, and operating life, particularly at extremely high rates ofrotation which have become essential in present engine designs.

Another object of the invention is to attain the above ends and furtherprovide for the passage of cooling air through the blades of the turbinerotor in order that they will not be overtemperatured when driven by agas stream which is at an elevated level.

These ends are attained by a turbine rotor which comprises two axiallyspaced, generally parallel discs. These discs are joined by vanesformedintegrally therewith and extending radially thereof. A pluralityof blades are angularly spaced about and project from the peripheries ofthe discs.

In another aspect, the objects of the invention may be attained by arotor comprising a pair of discs having radial vanes therebetween. Oneof the discs is annular to define, in part, an inlet for cooling airwhich passes between the discs and then enters passageways in bladessecured to the discs.

Preferably lugs are formed as integral extensions of these vanes, beyondthe peripheries of the discs. These lugs span the discs and are alsointegral therewith. The lugs define tapered, dovetailed guideways,extending generally axially of the rotor. The blades have tangs on whichare formed bulbous tenons slidingly received by the guideways defined bythe lugs. The radial forces acting on the blades, as a result ofcentrifugal force, are taken as a tension loading on the lugs. Thisloading is transmitted as a tension loading into the discs and thevanes, and from the vanes as a shear loading into the discs, therebyattaining a high strength rotor structure.

It is further preferred that both discs be annular and that a shaftportion be formed integrally with the inner periphery of one of thediscs and extend through the other disc in an axial direction forconnection with an element to be rotated thereby. The inner periphery ofthe other disc is spaced from this shaft portion to define an inlet forcooling air to pass between said disc to said blades. The vanes functionto pump the cooling air and assure a continuous flow thereof throughpassageways provided in the blades. The entrances of the bladepassageways are formed at the base of the tangs in communication withthe passageways defined by the vanes.

The above and other related objects and features of the invention willbe apparent from a reading of the following description of thedisclosure found in the accompanying drawings and the novelty thereofpointed out in the appended claims.

In the Drawings:

FIG. 1 is a longitudinal section through a turbine embodying the presentinvention;

FIG. 2 is a fragmentary view partially in section taken generally online IIII in FIG. 1;

FIG. 3 is a section, on an enlarged scale, taken generally on lineIll-Ill in FIG. 2;

FIG. 4 is a perspective view, on a further enlarged scale, ofa portionofthe turbine rotor with portions thereofbroken away and in section; and

FIG. 5 is a fragmentary perspective view of the portion of the turbinerotor which defines the inlet for cooling air passing therethrough.

Gas turbine engines conventionally comprise an axial flow compressorwhich discharges compressed air to a combustor to generate a hot gasstream. In FIG. 1 duct walls 10 and 12 represent the structure whichdefines the annular flow path of such a hot gas stream discharged from acombustor. Nozzles 15 direct this hot gas stream to drive a turbine 14which comprises a plurality of blades 20 projecting from a rotor 22. Therotor 22 is connected to a tubular shaft 16 which is appropriatelyjournaled, with bearing 18 supporting the aft end of the shaft relativeto a frame member 19. The shaft 16 is in turn connected to the rotor(not shown) of the axial flow compressor of the gas turbine engine. Theturbine 14 thus performs the usual function of driving the compressorrotor of a gas turbine engine.

The rotor 22 is preferably integrally formed and comprises a tubularshaft portion 24, having a flange 26 through which bolts 28 extend insecuring the turbine rotor to the drive shaft 16. An annular disc 30extends radially outwardly from the tubular shaft portion 24. A seconddisc 32 is joined to the disc 30 by integral vanes 34, which extendradially outwardly. Bulbous lugs 36 are formed beyond the outerperipheries of the discs 30 and 32 as integral continuations of thevanes 34. The lugs 36 also span the discs 30, 32 and are integraltherewith. Adjacent lugs 36 define tapered dovetail guideways or slotswhich receive correspondingly shaped bulbous tangs or tenons 38 formedon the blades 20. As will be evident from FIGS. 3 and 4, the slotsdefined by the lugs 36 are preferably arcuate and approximate theoutline of the airfoil shaped blades 20.

The blades 20 are axially retained in the rotor 22 by retainer plates 40and 42. The plates 40 and 42 are secured to the rotor 22 by bolts 44which extend through the lugs 36. The retainer plates 40, 42 also havelips 46, 48 which engage shoulders on the discs 32, 30 respectively. Theplates 40 and 42 also extend outwardly to platforms 50 which define theinner surface of the hot gas stream flow through the turbine wheel. Theplatforms 50 are cut away at one end to facilitate assembly of theblades into the arcuate guideways on the rotor. Plate 40 has fingers 51which fill in these cut away portions of the platforms. It will also beseen that the retainer plate 40 has a labyrinth seal member 52 formedintegrally therewith. This seal minimizes flow of hot gases into achamber 54 which is connected to a source of cooling air usually derivedfrom the engine compressor.

This cooling air is employed to prevent overtemperaturing of the blades20. Cooling air enters an annular inlet 56 defined by the innerperiphery of the disc 32 and the shaft portion 24. An inducer comprisingblades 58 integral with rings 60 (FIG. 5) is mounted in the inlet 56 bymeans of a snapring 62 and facilitates entry of air between the discs 30and 32. The vanes 34 then function to pump the cooling air toward theblades 20. This cooling air then passes through passageways 64 in thetangs 38, circulates through the hollow interior of the blades 20 and isdischarged through the outer ends of the blades into the hot gas stream.It will, of course, be evident that other forms of blades having coolingpassageways therein or therethrough may also be employed.

The described construction of rotor 22 not only provides an effectivemeans for conveying cooling air to the blades 20, but of equal, if notgreater, importance are its structural features which enable substantialsavings in weight for any given set of operating parameters.

In discussing these structural features, it will first be pointed outthat turbine rotor speeds are desirably extremely high, particularly infinely tuned gas turbine engines used for aircraft propulsion. Thestresses induced into the rotor 22 as a result of centrifugal force farexceed the stresses attributable to the torque which is to betransmitted to the compressor shaft. These centrifugal forces thus arethe limiting parameter in providing sufficient strength in the rotor 22.

Considering first the centrifugal forces on the blades 20, such forcesare carried in tension through the narrow neck n (FIG. 4) at the base ofthe tangs 38. The arcuate shape (approximating that of the blades 20) ofthese tangs minimizes stress levels as substantially all loading istaken in tension. The mating, tapered, tenon and dovetail portions ofthe tangs 38 and lugs 36 mutually load each other in compression as theradial forces are transmitted in shear to the lugs 36. The radial stresson the lugs 36 is distributed as a tension loading throughout theiraxial width across their bases b. The bases b blend with the outerperipheries of the discs 30, 32 so that a portion of the radial stresseson the lugs 36 is carried as a radial tension loading on the discs 30,32. The remainder of the radial stresses on the lugs 36 is carried as atension loading on the vanes 34. This tension loading of the vanes 34 isthen transmitted to the discs 30, 32 by a shear loading which isdistributed over a relatively wide area to minimize stress values.Dotted lines a in FIG. 4 illustrate the approximate shear stressdistribution between the discs 30, 32 and vanes 34 resulting from radialforces on the latter. It will be noted that the shear stress attenuatesradially inwardly of the discs 30, 32. The width of the vanes 34 is madegreatest at the outer peripheries of the discs 30, 32 where shear forcesare greatest (see also FIG. 1). The vanes then taper to a narrower widthas the shear forces decrease. In this fashion unit stress is minimizedand at the same time weight is also minimizedv The vanes 34 continueradially inwardly, with a constant width, beyond a point where the shearstresses are attenuated, in order to give further rigidity to the discs30, 32 which are joined thereby.

The described integral construction of the rotor 22 assures that radialstresses are taken in substantially pure tension or in shear over arelatively large area. This is also true as to any stresses which wouldbe generated in the event there were differential radial expansion ofthe discs 32 either because of centrifugal force or thermal differences.

Another factor to be considered is that the extreme rates of rotationproduce very high tangential hoop forces on the discs 30, 32. Thedescribed construction minimizes the resultant hoop stress byessentially eliminating any cause of stress concentration. Thus it willbe noted that the annular discs 30, 32 have structural integrity, beingfree of any holes, notches or the like which would cause stressconcentrations. in this connection, while the lugs 36 are integrallyformed with the discs 30, 32, they arenot a structural componentthereof, in that they are not subjected to tangential hoop loading. Thusthe provision of holes for the bolts 44, through these lugs, does notweaken the rotors ability to withstand the hoop stress resulting fromcentrifugal forces.

It is preferred that the rotor 22 be integrally formed, as described.This, however, does not mean that the rotor must initially comprise asingle element. For example, the disc 32 and a portion of the vanes 34could be separately fabricated and the vanes then joined by brazing,diffusion, bonding, or the like.

Thus it will be recognized that these and other variations from thedescribed embodiment are within the scope of the present inventiveconcepts which is to be derived solely from the claims herein.

Having thus described the invention, what is claimed as novel anddesired by Letters Patent of the United States is:

We claim:

1. A rotor comprising:

two axially spaced, generally parallel discs;

radially extending vanes integral with the discs, disposed between saiddiscs and joining said discs together;

a plurality of blades projecting from and angularly spaced about theperiphery of said discs; and

said blades being connected to said vanes whereby radial centrifugalforces on the blade will be taken, at least in part, as a tensionloading on the vanes, which, in turn, is transmitted as a shear loadingto the discs over a relatively large area.

2. A rotor as in claim 1 wherein:

lugs are formed as integral extensions of said vanes beyond theperipheries of said discs, said lugs further spanning said discs andbeing integral therewith;

said lugs defining tapered, dovetail guideways extending generallyaxially of said rotor and, further wherein; said blades have tangs withtapered tenons slidingly received by said guideways; and

whereby radial forces acting on said blades are taken as a tensionloading on said lugs which is transmitted as a tension loading into saiddiscs and vanes and from said vanes as a shear loading into said discs.

3. A rotor as in claim 1 wherein both discs are annular:

a shaft portion is integral with the inner periphery of one disc andextends in an axial direction through said other disc for connectionwith an element to be rotated thereby; and

the inner periphery of said other disc being spaced from said shaftportion to define an inlet for cooling air to pass between said disc tosaid blades.

4. A rotor as in claim 1 wherein:

lugs are formed as extensions of said vanes beyond the peripheries ofsaid discs, said lugs further spanning said discs and being integraltherewith, said lugs defining tapered, dovetailed guideways extendinggenerally axially of said rotor;

said blades have tangs with tapered tenons slidably received by saidguideways;

whereby radial forces acting on said blades are taken as a tensionloading on said lugs which is transmitted in tension directly into saiddiscs and vanes and from said vanes as a shear loading into said discs,and further wherein;

both of said discs are annular;

a shaft portion is integral with the inner periphery of one disc andextends in an axial direction through said other disc for connectionwith an element to be rotated thereby;

the inner periphery of said other disc being spaced from said shaftportion to define an inlet for cooling air to pass between said discs tosaid blades;

said blades having air cooling passageways extending from the bases ofsaid tangs therethrough; and

whereby cooling air entering said inlet will be pressurized by thepumping action of said vanes to be discharged through said bladepassageways.

5. A rotor as in claim 4 wherein, said vanes have a maximumcross-sectional width at the bases of said lugs and are progressivelytapered to a narrower cross-sectional width as they extend inwardly to apoint where the shear loading thereon is substantially attenuated, saidvanes having a substantially uniform cross-sectional thickness inwardlyfrom such point and continuing to the inner periphery of said otherdisc.

6. A rotor as in claim 4 wherein, said discs are solid from their innerto their outer peripheries.

